NASA Technical Reports Server (NTRS) 20050210102: Genesis Noble Gas Measurements
Publication date 2005-08-19
Topics NASA Technical Reports Server (NTRS), GENESIS MISSION, GAS ANALYSIS, FLAT SURFACES, RARE GASES, REFRACTORY MATERIALS, ELECTROSTATICS, GAS SPECTROSCOPY, LASER ABLATION, MASS SPECTROMETERS, METAL VAPORS, PHOTOMULTIPLIER TUBES, SOLID SURFACES, Hohenberg, Charles M.,
The original thrust of our Genesis funding was to extend and refine the noble gas analytical capabilities of this laboratory to improve the precision and accuracy of noble gas measurements in order to optimize the scientific return from the Genesis Mission. This process involved both instrumental improvement (supplemented by a SRLIDAP instrument grant) and refinement of technique. The Genesis landing mishap shifted our emphasis to the irregular aluminum heat shield material from the flat collector wafers. This has required redesign of our laser extraction cells to accommodate the longer focal lengths required for laser extraction from non-flat surfaces. Extraction of noble gases from solid aluminum surfaces, rather than thin coatings on transparent substrates has required refinement of controlled-depth laser ablation techniques. Both of these bring new problems, both with potentially higher blanks form larger laser cells and the larger quantities of evaporated aluminum which can coat the sapphire entrance ports. This is mainly a problem for the heavy noble gases where larger extraction areas are required, necessitating the new aluminum vapor containment techniques described below. With the Genesis Mission came three new multiple multiplier noble gas mass spectrometers to this laboratory, one built solely by us (Supergnome-M), one built in collaboration with Nu-Instruments (Noblesse), and one built in collaboration with GVI (Helix). All of these have multiple multiplier detection sections with the Nu-Instruments using a pair of electrostatic quad lenses for isotope spacing and the other two using mechanically adjustable positions for the electron multipliers. The Supergnome-M and Noblesse are installed and running. The GVI instrument was delivered a year late (in March 2005) and is yet to be installed by GVI. As with all new instruments there were some initial development issues, some of which are still outstanding. The most serious of these are performance issues with the miniature channel electron multipliers. The delayed installation of Helix by the GVI is partly due to failure of the initial batch of Burle channel multipliers to perform as expected. A number of the channel multipliers designed for Noblesse by Burle have also failed upon baking. Burle has now refined the design of these and we have installed two of the new multipliers and are assessing their performance. The remaining multipliers Will be upgraded to the new design from Burle once we confirm that the problem has been fixed.
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